Hypodermic syringes are widely used in the medical field for administering medicaments and for drawing body fluid samples. Generally, hypodermic syringes include a needle having a sharpened distal point for penetrating vial stoppers or patient's skin. The needle is attached either fixedly or removably to a syringe barrel. Hypodermic syringes and needles have been used for many years with few problems reported when the vast numbers and needles being used are considered. More recently, with the recognition of viral diseases that are transmitted by body fluids and greater sensitivity of the need to protect health care workers from inadvertent contact with previously used needles (commonly referred to as “sharps”) as well as the need to reduce criminal misuse of improperly disposed of needle and syringes, syringes and needles that include provisions to prevent reuse have been developed.
Devices intended to prevent reuse of needles and syringes include a variety of sharps collector systems that are widely used in health care facilities. Other developments include needle attachments that may be readily broken off by practitioners once the syringe has completed its intended use. A variety of shielding mechanisms has been developed; some of which are currently commercially available. While many of these developments have reduced the incidence of inadvertent exposure of healthcare workers to sharps, many of these devices can be overcome by an individual determined to obtain and misuse a hypodermic syringe and needle. As a result of this problem, further developments in the art of hypodermic syringes have resulted in syringes with needles that withdraw into the body of the syringe once their intended use is completed.
Current conventional syringes are considered by users to be virtually fault-free and reliable. They are used for a variety of different procedures involving both “one-shot” fill and inject procedures, as well as more complex mixing, measuring and delivery functions. In order for a retracting needle syringe to replace these functional, utilitarian and reliable conventional syringes, the retracting needle syringe should not significantly interfere with the users' current practices, it needs to be substantially reliable and its cost should not be prohibitive. Current conventional syringes are often manufactured at rates of several hundred per minute and their cost is generally not a significant factor in their usage. Additionally every year, hundreds of millions of small capacity (one milliliter) syringes are used outside of the normal controlled health care environment by diabetics and other self-injectors who must daily accurately inject small amounts of medication or other liquid, often only a few tenths of a milliliter. These small capacity syringes are usually physically small, with an overall length of less than five inches and an inside bore diameter of about one-quarter inch. In light of the discussions above, one skilled in the art of high volume manufacturing recognizes that assembling hundreds of millions of most of these relatively complex devices with their retraction elements contained in such a small space as a one-quarter inch diameter bore is a difficult task.
The need thus exists for a selectively retracting needle syringe that is compatible with a small capacity syringe without retracting needle features, that is capable of being manufactured at high volumes and is sufficiently non-complex to be reliable in use when produced at volumes of hundreds of millions per year. Such a device is disclosed in U.S. Pat. Nos. 6,432,087; 6,679,863 and 6,689,106. The invention disclosed herein represents an improvement of the plunger and stopper of the syringes described in the aforementioned U.S. patents and any other design of single-use syringe using a barrel or needle assembly based cutting element intended to cut through the stopper and the plunger from the distal end of the plunger rod assembly.